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Spectroscopy Observing Programme

The splitting of light into it's component parts, the spectrum, and especially the study of absorption and emission lines, can tell Astronomers the composition, density and temperature of an object such as a star or nebulae.
In recent years, with the advent of CCD and CMOS detectors amateur astronomers have been able to study spectroscopy, a science, which only recently was the domain of large telescopes and professional astronomers.
At Crayford we are starting up the Spectroscopy observation programme for any member who wishes to participate in this subject.
SpectrumLine.jpg

Getting Started:

Equipment

The basic set-up is a telescope, diffraction grating or prism, and a detector (web cam, digital camera or CCD).

Diffraction gratings can be bought cheaply and mounted as described by Martin in his presentation to the Society in January 2009, alternatively a cheap basic set-up can be bought in the form of a Star Analyser, this grating fits the same way as a 1.25" filter.

A 'free', experimental, full aperture grating can be downloaded from the COAA website, the disadvantage of this grating is the lack of blazing, I can confirm that with my printer set to 800dpi and the printer set to print lines 3 dots wide and gaps 3 dots wide you do indeed get a spectra (tested with binoculas).

A more sophisticated set-up, designed by amateurs to do real science is the LHIRES III spectrograph from www.shelyak.com it is not cheap but probably gives the best value for money among the commercial offerings and is becoming the de-facto standard for amateur astronomers.

DIY Spectrascopes

DVD and CD's are commenly used to make DIY spectrascopes, these work because the lines between each track are very close together, just like a diffraction grating.
CD 1.6µm between lines
DVD 0.74µm between lines
SPECTROSCOPY_DVD.jpg

Here are instructions for a Solar spectrascope made from cardboard and a CD/DVD, 'big' Andy and Simon have made these in the past and they work well for educational use, you can see the Fraunhoffer lines and the spectra of energy saving light bulbs. Martin has made a solar spectrascope from a DVD and DVD case which also works well, the instructions for this can be found here


SPECTRASCOPYMC01.jpg
Martin gave a talk at society night on making a simple spectrascope using a 300 lines per mm transmission grating as used in many schools this can be found here



Software

You will need software to process and analyse your spectra, we are still at the early stages of assessing the best software and techniques, but the following look promising candidates...
  • AIP4Win2 – many members have this superb book and software.
In AIP4Win2 you can convert a spectrum into a text file that can be used in Open Office or MS Excel to produce a graph.
In Visual spec you can calibrate your set-up and identify emission/absorbtion lines.

A graphics programme such as the Freeware GIMP or Photoshop can be used to select a single line in the spectrum that can then be stretched to give a traditional looking spectra. such as the one for Betelgeuse Simon captured below (using AIP4Win2, Open Office and GIMP).

SPECT_betelgeuse_SD1.jpg
Spectrum of Betelgeuse taken with a Star Analyser, F4 300mm Newtonian and Artemis CCD

More Information

There are a number of sources of information for amateur astronomers not the least the presentation by Robin Leadbeater given at a BAA VSS workshop.
SpectrumLine.jpg

Objects in the Observing Programme


First Steps:
To get to know your equipment and software I would recommend you point your spectroscope at any of these bright stars or this slightly longer list, that includes the spectral type - although note, we have found some of these stars are too bright! Resulting in very short exposures.

A primary goal of the observing programme is to learn more about spectra and the techniques to capture them so that we may use them effectiely on interesting objects, to this end, in the early days of the programme and for observers new to spectroscopy we recommend completing the spectral sequence and identifying some of the important lines.

Bright Stars


First Light for Simon!

My first attempt, the stars are not as well focused as I would like and I think the very short exposures (0.1s) have resulted in capturing the scintillation of the stars being observed resulting in wider lines than I think are possible with my set-up.
SPECT_SD_FirstLight25.JPG
Click on the Image for a larger view

First Light for Martin!

Martin's first attempt at spectroscopy on bright Stars
spectra_of_bright_Stars_MC01t.jpg
Click on the Image for a larger view

Orion Nebula (M42)


Imaging nebulae, like the Orion Nebula, shows why H alpha and OIII filters can really help in our light polluted skies.
SPECTRA_M42.JPG
DSLR Single Frame, 30s Exposure, limiting naked eye magnitude vMag = 4 By Simon Dawes

Comet C/2007 N3 Lulin


cometLulinspectraMC01.jpg
Note the spectra from the comet’s tail is different from the coma, the tail emitting prominently in the Blue/green end of the spectrum.

Page edited 29 times. Last edit by - SimonTelescopium SimonTelescopium on May 10, 2010 1:41 pm. This site contains 463 pages
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CMHAS - Spectroscopy